DNA sequences which lead to the formation of levans plasmids containing these sequences as well as a process for preparing transgenic plants

ABSTRACT

There are described DNA sequences, which lead to the formation of levans, plasmids containing these DNA sequences, as well as a process using these plasmids for preparing transgenic plants with levan accumulation.

FIELD OF THE INVENTION

The present invention relates to DNA sequences which lead to the formation of polyfructans (levans), as well as a process for preparing transgenic plants using plasmids on which these DNA sequences are located.

High molecular weight, water soluble, linear polymers, for example those based on polyacrylates or polymethacrylates, are products of mineral oils and have many important uses. In particular their properties in increasing the viscosity of aqueous systems, in suspending or sedimentation acceleration and complexing are especially valuable from the technical viewpoint. These products are also used in exceptionally large amounts in super absorbers for water binding and in water dilutable lacquers. In spite of the outstanding positive properties, because such products are difficult to dispose of, their use is increasingly coming under criticism because they are not biodegradable.

Alternatives based on recyclable raw materials, especially starches and cellulose, because of the macromolecular structure of these polysaccharides, have been shown to have limited value. As a replacement for non-biodegradable chemically derived polymers, a number of derivatised high polymeric polysaccharides have been considered. Until now, such polysaccharides could only be obtained biotechnologically via suitable fermentation and transglycosidation processes. The products obtained in this way, such as dextrans and polyfructans (levans) are not competitive as raw materials for mass production.

Polyfructans are found in a number of monocotyledonous and dicotyledonous higher plants, in green algae as well as in a number of gram positive and gram negative bacteria (Meier and Reid, (1982) Encyclopedia of Plant Physiology, New Series, 13A. 418-471). The role of fructans for the plant development and plant growth is not fully understood. Functions of the fructans that have been proposed are as a protectant against freezing at low temperatures, as alternative carbohydrate stores which limit starch biosynthesis, as well as applied intermediary stores for photoassimilates, which are situated in the stems of grasses shortly before their transfer into the seeds.

All fructans contain, as starter molecule for the polymerisation reaction, a molecule of sucrose (glucose-fructose) to which fructose polymers are added.

Depending on the coupling of the fructose molecule, fructans of plant origin can be classified into four classes (Meier and Reid (1982), Encyclopedia of Plant Physiology, New Series, 13A, 418-471):

a) (2-1) coupled β-D-fructans (inulin type)

b) (2-6) coupled β-D-fructans (phlein or levan type)

c) highly branched fructans with a mixture of 2-1 and 2-6 couplings.

d) (2-1) coupled β-D-fructans, which in contrast to the types under a-c, are added completely from fructose residues of polymerisation both from glucose and also from fructose residues from polyfructose residues (neokestose type).

Fructans of bacterial origin correspond either to the levan or to the inulin type (Carlsson (1970) Caries Research 4, 97-113) and Dedonder (1966) Methods Enzymology 8, 500-505).

Experiments on the biosynthesis of fructans in plants and bacteria lead one to conclude that the biosynthesis proceeds by various routes. Bacterial and plant fructans are further distinguished, not particularly in their primary structure but mainly in their molecular weight. Thus, fructans isolated from plants have been shown to have molecular weights of between 5000 and 50,000 d (Pollock and Chatterton (1988) in: The Biochemistry of Plants 14, 109-140), while fructans isolated from bacteria, molecular weights of up to 2,000,000 d have been described (Clarke et al (1991) in: Carbohydrates as Organic Raw Materials, VCH Weinheim, 169-182).

Various microorganisms from the group of Bacillus spp as well as Streptococcus spp produce polyfructoses in which both fructans of the levan type and fructans of the inulin type have been described (Carlsson (1970) Caries Research 4, 97-113 and Dedonder (1966) Methods Enzymology 8, 500-505).

Experiments on biosynthesis pathways have made it clear that, in comparison to biosynthesis pathways in higher plants, there is a more simple pattern and a sharing of only one enzyme. This enzyme with the trivial name levan sucrase is a transfructosylase (sucrose:β-D-fructosyl transferase, E.C.2.4.1.10.), which catalyses the following reaction:

    sucrose+acceptorglucose+fructosyl acceptor

Representative acceptors are water, alcohol, sugar or polyfructoses. The hypothesis that only one enzyme catalyses this reaction, depends on the one hand on the examination of the protein chemically purified enzyme, and on the other, to the fact that the gene for levan sucrase has been isolated from various Bacillus spp. as well as from a Streptococcus spp. and after transfer into E. coli leads to the formation of levan in E. coli (Gay et al (1983) J. Bacteriology 153, 1424-1431 and Sato et al. (1986) Infection and Immunity 52, 166-170).

Until now, genes for levan sucrase from Bacillus amyloliquefaciens (Tang et al. (1990) Gene 96, 89-93) and Bacillus subtilis (Steinmetz et al. (1985) Mol. Gen. Genetics 200, 220-228), have been described, and demonstrate relatively high homology with each other and both of which catalyse the synthesis of fructans of the levan type. Further a fructosyl transferase from Streptococcus mutans (Shiroza et al. (1988) J. Bacteriology 170, 810-816) has been described. This shows little homology to either levan sucrases from Bacillus spp. The fructan formed in Streptococcus mutans is of the inulin type.

In WO 89/12386, there is described the possibility of producing carbohydrate polymers such as dextran or levan in transgenic plants, especially in the fruit of transgenic plants. To prepare these plants, the use of levan sucrases from Aerobacter levanicum, Streptococcus salivarius and Bacillus subtilis and the use of dextran sucrases from Leuconostoc mesenteroides have been described.

Further the construction of chimeric genes is described which may be suitable for the expression of the levan sucrase from Bacillus subtilis as well as the dextran sucrase from Leuconostoc mesenteroides in transgenic plants. Also described is the preparation of transgenic plants containing these constructs. Further, the preparation of transgenic plants that contain these constructs are described. Whether polyfructans can actually be produced by the described process is not known.

There is also described a series of processes for modifying the carbohydrate concentration and/or concentrating carbohydrates in transgenic plants by means of biotechnological methods. Thus, in view of the fact that increasing of the starch concentration and the modification of the starch in physical and chemical respects is already known, then a modification of the carbohydrate content of potato plants by raising or lowering the ADP-glucose-pyrophosphorylase activity can be achieved (EP 455 316).

From EP 442 592 it is further known that a modification of the distribution of photoassimilates by means of cytosolic and apoplastic invertase is possible and that the yield as well as the drought and frost resistance of potato plants can be modified through the expression of a heterologous pyrophosphatase gene in potato plants.

In order to adapt the physico-chemical parameters of raw materials which are increasingly being used, such as polysaccharides, to the requirements of the chemical industry, as well as to minimise the costs of obtaining these products, processes for the preparation of transgenic plants have to be developed which lead in comparison with known processes to better, higher yielding plants.

SUMMARY OF THE INVENTION

It has now been surprisingly found that the DNA sequence of the levan sucrase from a gram-negative bacterium of the species Erwinia amylovora with the nucleotide sequence (Seq-ID NO 1): ##STR1## makes possible the preparation of large amounts of polyfructans (levans) in transgenic plants, which decisively meet the needs of the chemical industry in respect of recyclable raw materials.

By integration of a DNA sequence in a plant genome, on which the above given DNA sequence is located, the polyfructan (levan) expression in plants, especially in leaves and tubers is made possible. The levan sucrase of the invention shows, at the DNA level, no significant homology to the known levan sucrases.

The invention further provides a process for the preparation of transgenic plants with polyfructan (levan) expression in leaves and tubers that comprises the following steps:

(a) preparation of a DNA sequence with the following partial sequences:

i) a promoter which is active in plants and ensures formation of an RNA in the intended target tissues or target cells,

ii) a DNA sequence of a levan sucrase, and

iii) a 3'-non-translated sequence, which in plant cells leads to the termination of the transcription as well as the addition of poly A residues to the 3'-end of the RNA,

(b) transfer and integration of the DNA sequence in the plant genome of a recombinant double stranded DNA molecule from plant cells using a plasmid, and

(c) regeneration of intact whole plants from the transformed plant cells.

The levan sucrase obtained in process step (a,) ii) preferably shows the nucleotide sequence noted under Sequence ID No 1.

The levan sucrase catalyses the following reaction:

    Sucrose-(fructose).sub.n +sucrosesucrose-(fructose).sub.n+1 +glucose.

Using this process in principle, all plants can be modified in respect to a polyfructan (levan) expression, preferably crops such as maize, rice, wheat, barley, sugar beet, sugar cane, tobacco and potatoes.

In process step (b), in principle, all plasmids can be used which have the DNA sequence given under sequence ID No 1. Preferably used are plasmid p35s-CW-LEV (DSM) 7186), plasmid P35s-CY-LEV (DSM 7187) or plasmid P33-CW-LEV (DSM 7188).

Since sucrose represents the substrate for the levan sucrase, the production of polyfructans is especially advantageous in those organs which store large amounts of sucrose. Such organs are for example, the roots of sugar beet or the stems of sugar cane. It is especially useful in genetically modified potatoes, which store sucrose in their tubers, through the blocking of starch biosynthesis.

Biosynthesis of sucrose takes place in the cytosol, while in contrast, storage is in the vacuole. During transport into the storage tissues of a sugar beet or potato or into the endosperm of seeds, the sucrose must cross the intercellular space. In the production of polyfructans, all three cell compartments are suitable, i.e. cytosol, vacuole and intercellular space.

The coding sequence of the levan sucrase of the nucleotide Sequence ID No 1 can be provided with a promoter that ensures the transcription occurs in a specified order and which is coupled in sense orientation (3'-end of the promoter to the 5'-end of the coding sequence) onto the coding sequence which codes for the enzyme to be formed. The termination signal which determines the termination of the mRNA synthesis is adhered to the 3'-end of the coding sequence. In order to direct the enzyme which is expressed in specified sub-cellular compartments such as chloroplasts, amyloplasts, mitochondria, vacuoles, cytosol or intercellular space, a so-called signal sequence or a transit peptide coding sequence can be positioned between the promoter and the coding sequence. This sequence must be in the same reading frame as the coding sequence of the enzyme.

For the introduction of the DNA sequence of the invention in higher plants, a large number of cloning vectors are available which contain a replication signal for E. coli and a marker which allows a selection of the transformed cells. Examples of vectors are pBR 322, pUC-series, M13 mp-series, pACYC 184; EMBL 3 etc.. According to the introduction method of the desired gene in the plant, other DNA sequences may be suitable. Should the Ti- or Ri-plasmid be used, e.g. for the transformation of the plant cell, then at least the right boundary, often however both the right and left boundaries of the Ti- and Ri-Plasmid T-DNA, is attached, as a flanking region, to the gene being introduced. The use of T-DNA for the transformation of plants cells has been intensively researched and is well described in EP 120 516; Hoekema, In: The Binary Plant Vector System, Offset-drukkerij Kanters B.V. Alblasserdam, (1985), Chapter V; Fraley, et al., Crit. Rev. Plant Sci., 4:1-46 and An et al. (1985) EMBO J. 4: 277-287. Once the introduced DNA is integrated in the genome, it is as a rule stable there and remains also in the offspring of the original transformed cells. It normally contains a selection marker, which induces resistance in the transformed plant cells against a biocide or antibiotic such as kanamycin, G 418, bleomycin, hygromycin or phosphinotricin, etc. The individual marker employed should therefore allow the selection of transformed cells from cells which lack the introduced DNA.

For the introduction of DNA into a plant, besides transformation using Agrobacteria, there are many other techniques available. These techniques include the fusion of protoplasts, microinjection of DNA and electroporation, as well as ballistic methods and virus infection. From the transformed plant material, whole plants can be regenerated in a suitable medium which contains antibiotics or biocides for the selection. The resulting plants can then be tested for the presence of introduced DNA. No special demands are placed on the plasmids in injection and electroporation. Simple plasmids, such as e.g. pUC-derivatives can be used. Should however whole plants be regenerated from such transformed cells the presence of a selectable marker gene is necessary. The transformed cells grow within the plants in the usual manner (see also McCormick et al.(1986) Plant Cell Reports 5: 81-84). These plants can be grown normally and crossed with plants that possess the same transformed genes or different. The resulting hybrid individuals have the corresponding phenotypical properties.

Deposits

The following plasmids were deposited at the Deutschen Samnlung von Mikroorganismen (DSM) in Braunschweig, Germany on the 16.07.1992 (deposit number):

Plasmid p35s-CW-LEV (DSM 7186)

Plasmid p35s-CY-LEV (DSM 7187)

Plasmid p33-CW-LEV (DSM 7188)

DESCRIPTION OF THE FIGURES

FIG. 1 shows the structure of the p35-CW-LEV plasmid. It comprises the three fragments A, B and C. Fragment A contains the 35s promoter of the cauliflower mosaic virus (CaMV), nucleotides 6906-7437.

Fragment B contains the sequence of the nucleotides 689-2122 of the levan sucrase from Erwinia amylovora (Seq. ID No.1).

Fragment C contains the polyadenylation signal of the gene 3 of the T-DNA of the Ti-plasmid, pTi ACH 5, nucleotides 11749-11939.

FIG. 2 shows the structure of the p35s-CY-LEV plasmid. It comprises the three fragments A, B and C. Fragment A contains the 35s promoter of the cauliflower mosaic virus (CaMV), nucleotides 6909-7437.

Fragment B contains the sequence of the nucleotides 864-2122 of the levan sucrase from Erwinia amylovora (Seq. ID No.1).

Fragment C contains the polyadenylation signal of the gene 3 of the T-DNA of the Ti-plasmid, pTi ACH 5.

FIG. 3 shows the structure of the p33-CW-LEV plasmid. It comprises the three fragments A, B and C.

Fragment A contains the DraI-DraI-fragment (position -1512 to position +14) of the promoter region of the patatin gene B33.

Fragment B contains the sequence of the nucleotides 689-2122 of the levan sucrase from Erwinia amylovora (Seq. ID No.1).

Fragment C contains the polyadenylation signal of the gene 3 of the T-DNA of the Ti-plasmid, pTi ACH 5, nucleotides 11749-11939.

FIG. 4 shows the detection of polyfructan in transformed tobacco plants (No. 2, 3 and 13).

In this:

Fru=fructose, Suc=sucrose, Kes=kestose

c1=control 1, c2=control 2, M=marker

FIG. 5 shows NMR peaks for levan extracted from transformed plants.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to understand the examples forming the basis of this invention all the processes necessary for these tests and which are known per se will first of all be listed:

1. Cloning process

The vector pUC 18 (Yanisch-Perron et al. (1985) Gene 33: 103-119) was used for cloning.

For the plant transformations, the gene constructs were cloned in the binary vector BIN 19 (Bevan (1984) Nucl. Acids Res 12: 8711-8720)

2. Bacterial strains

The E. coli strain-BMH71-18 (Messing et al., Proc. Natl. Acad. Sci. USA (1977), 24, 6342-6346) or TB1 was used for the pUC vectors. TB1 is a recombinant-negative, tetracycline-resistant derivative of strain JM101 (Yanisch-Perron et al., Gene (1985), 33, 103-119). The genotype of the TB1 strain is (Bart Barrel, personal communication): F'(traD36, proAB, lacI, lacZΔM15), Δ(lac, pro), SupE, thiS, recA, Sr1::Tn10(TcR).

The transformation of the plasmids into the potato plants was carried out using Agrobacterium tumefaciens strain LBA4404 (Bevan, (1984), Nucl. Acids Res. 12, 8711-8720).

3. Transformation of Aarobacterium tumefaciens

In the case of BIN19 derivatives, the insertion of the DNA into the Agrobacterium was effected by direct transformation in accordance with the method of Holsters et al., (1978) (Mol Gene Genet 163: 181-187). The plasmid DNA of the transformed Agrobacterium was isolated in accordance with the method of Birnboim and Doly (1979) (Nucl Acids Res 7: 1513-1523) and was analysed by gel electrophoresis after suitable restriction cleavage.

4. Plant transformation

A) Tobacco: 10 ml of an overnight culture of Agrobactenium tumefaciens, grown under selection, were centrifuged off, the supernatant was discarded, and the bacteria were resuspended in the same volume of antibiotic-free medium. In a sterile petri dish, leaf discs of sterile plants (approximately 1 cm²), the central vein of which had been removed, were immersed in this bacterial suspension. The leaf discs were then placed in a closely packed arrangement in petri dishes containing MS medium (Murashige et al. (1962) Physiologia Plantarum 15, 473-497) with 2% sucrose and 0.8% bacto agar. After two days incubation in the dark at 25 °C., they were transferred onto MS medium containing 100 mg/l kanamycin, 500 mg/l claforan, 1 mg/l benzylaminopurine (BAP), 0.2 mg/l of naphthylacetic acid (NAA) and 0.8% bacto agar. Growing shoots were transferred onto hormone-free MS medium with 250 mg/l of claforan.

B) Potato: Ten small leaves, wounded with a scalpel, of a sterile potato culture were placed in 10 ml of MS medium with 2% sucrose containing 30-50 μl of an Agrobacterium tumefaciens overnight culture grown under selection. After 3-5 minutes gentle shaking, the leaves were laid out on MS medium of 1.6% glucose, 2 mg/l of zeatin ribose, 0.02 mg/l of naphthylacetic acid, 0.02 mg/l of gibberellic acid, 500 mg/l of claforan, 50 mg/l of kanamycin and 0.8% bacto agar. After incubation for one week at 25° C. and 3000 lux, the claforan concentration in the medium was reduced by half. Further cultivation was carried out using the method described by Rocha-Sosa et al. (1989) EMBO Journal 8, 29).

5. Analysis of genomic DNA from transgenic plants

The isolation of genomic plant DNA was carried out according to Rogers et al. (1985) Plant Mol Biol 5, 69-76).

For the DNA analysis, after suitable restriction cleavage, 10 to 20 μg of DNA were analysed, by means of Southern blotting, for the integration of the DNA sequences to be investigated.

6. Analysis of the total RNA from transgenic plants

The isolation of plant total RNA was carried out according to Logemann et al. (1987), Analytical Biochem. 163, 16-20.

For the analysis, 50 μg portions of total RNA were investigated, by means of Northern blotting, for the presence of the transcripts sought.

7. Extraction and determination of polyfructose in plants

The extraction and determination were carried out according to the method of Portis H. G. (1990), Meth. Plant Biochem. 2, 353-369.

EXAMPLE 1

Preparation of plasmid P35s-CW-LEV and insertion of the plasmid into the aenome of tobacco and potato

The plasmid p35s-CW-LEV comprises the three fragments A, B and C, which were cloned in the cutting sites for restriction enzymes of the polylinker from pUC 18 (see FIG. 1).

Fragment A contains the 35S promoter of cauliflower mosaic virus (CaMV). It contains a fragment that includes the nucleotides 6909 to 7437 of CaMV (Franck et al. (1980) Cell 21, 285-294) and was isolated as Eco RI-Kpn I fragment from plasmid pDH 51 (Pietrzak et al., Nucleic Acids Research 14, 5857-5868) and cloned between the Eco RI-Kpn I cutting sites of the polylinker of plasmid pUC 18.

Fragment B contains the sequence of the nucleotides 689-2122 of the gene of the levan sucrase from Erwinia amylovora (Seq. ID No.1) and was cloned between the BamHI/SalI cutting positions of the polylinker of pUC 18.

Fragment C contains the polyadenylation signal of the gene 3 of the T-DNA of the Ti-plasmid, pTi ACH 5 (Gielen et al (1984); EMBO J. 3, 835-846) nucleotides 11749-11939 which was isolated as Pvu II-Hind III fragment from the plasmid PAGV 40 (Herrera-Estrella et al (1983) Nature 303, 209-213) and, after addition of Sph I linkers to the Pvu II cutting positions, was cloned between the SphI-Hind III cutting positions of the polylinker of pUC 18.von pUC 18. The plasmid p35s-CW-LEV has a size of 2151 bp.

The part of the plasmid p35s-CW-LEV comprising the fragments A, B and C was introduced in binary vectors and using the Agrobacteria system was introduced into tobacco and potato plants. Intact plants were regenerated from transformed cells. The analysis of the leaves from a series of Tobacco plants transformed with this gene, clearly showed the presence of polyfructan (levan) which is traced back to the expression of the gene 35s-Cw-LEV (see FIG. 4).

EXAMPLE 2

Preparation of plasmid p35s-CY-LEV and insertion of the plasmid into the genome of tobacco and potato

This Example was carried out in an analogous manner to that described under Example 1, but with the modification, that the Fragment B (coding for the levan sucrase) is shortened on the nucleotides at the 5'-end. This results in the expression of the protein in the cytosol of transgenic plants.

The plasmid p35s-CY-LEV comprises the three fragments A, B and C, which were cloned in the cutting sites for restriction enzymes of the polylinker from pUC 18 (see FIG. 2).

Fragment A contains the 35S promoter of cauliflower mosaic virus (CaMV). It contains a fragment that includes the nucleotides 6909 to 7437 of CaMV (Franck et al. (1980) Cell 21, 285-294) and was isolated as Eco RI-Kpn I fragment from plasmid pDH 51 (Pietrzak et al., Nucleic Acids Research 14, 5857-5868) and cloned between the Eco RI-Kpn I cutting sites of the polylinker of plasmid pUC 18.

Fragment B contains the sequence of the nucleotides 864-2122 of the gene of the levan sucrase from Erwinia amylovora (Seq. ID No.1) and was cloned between the SmaI/SalI cutting positions of the polylinker of pUC 18.

Fragment C contains the polyadenylation signal of the gene 3 of the T-DNA of the Ti-plasmid, pTi ACH 5 (Gielen et al (1984); EMBO J. 3, 835-846) nucleotides 11749-11939 which was insolated as Pvu II-Hind III fragment from the plasmid pAGV 40 (Herrera-Estrella et al (1983) Nature 303, 209-213) and, after addition of Sph I linkers to the Pvu II cutting positions, was cloned between the SphI-Hind III cutting positions of the polylinker of pUC 18.von pUC 18. The plasmid p35s-CY-LEV has a size of 1976 bp.

The part of the plasmid p35s-CY-LEV comprising the fragments A, B and C was introduced in binary vectors and using the Agrobacteria system was introduced into tobacco and potato plants. Intact plants were regenerated from transformed cells.

EXAMPLE 3

Preparation of plasmid p35s-CY-LEV and insertion of the plasmid into the genome of tobacco and potato

This Example was carried out in an analogous manner to that described under Example 1, but with the 35s promoter being replaced with the promoter of the class I patatin Gene B33 (Rocha-Sosa et al, (1989) EMBO J 8, 23-29) The plasmid p33-CW-LEV comprises the three fragments A, B and C, which were cloned in the cutting sites for restriction enzymes of the polylinker from pUC 18 (see FIG. 3).

Fragment A contains the DraI-DraI fragment (position -1512 to position +14) of the promoter region of the patatin gene B33 (Rocha-Sosa et al (1989) EMBO J. 8, 23-29), which was cloned in the Sma I position of the polylinker of PUC 118.

Fragment B contains the sequence of the nucleotides 689-2122 of the gene of the levan sucrase from Erwinia amylovora (Seq. ID No.1) and was cloned between the BamHI/SalI cutting positions of the polylinker of pUC 18.

Fragment C contains the polyadenylation signal of the gene 3 of the T-DNA of the Ti-plasmid, pTi ACH 5 (Gielen et al (1984); EMBO J. 3, 835-846) nucleotides 11749-11939 which was insolated as Pvu II-Hind III fragment from the plasmid pAGV 40 (Herrera-Estrella et al (1983) Nature 303, 209-213) and, after addition of Sph I linkers to the Pvu II cutting positions, was cloned between the SphI-Hind III cutting positions of the polylinker of pUC 18.von pUC 18. The plasmid p33-CW-LEV has a size of 3149 bp.

The part of the plasmid p33-CW-LEV comprising the fragments A, B and C was introduced in binary vectors and using the Agrobacteria system was introduced into tobacco and potato plants. Intact plants were regenerated from transformed cells. The analysis of the leaves from a series of Tobacco plants transformed with this gene, clearly showed the presence of polyfructan (levan) which is traced back to the expression of the gene 33-CW-LEV.

EXAMPLE 4

Analysis of β2,6-D-Fructofurane (levan) synthesised in transgenic plants by 13C-NMR spectroscopy

The analysis of transgenic plants transformed with the construct p35s-CW-LEV is shown as an example. This analysis can equally be applied to transgenic plants transformed with the constructs p35S-CW-LEV or p35s-CY-LEV.

To obtain sufficient amounts of levan synthesised by transgenic plants to perform NMR spectroscopy, about 10 g. of leaf tissue was ground in 10 ml. of water. The homogenate is than centrifuged at 4000 Rpm in a Beckman Minifuge and the supernatant is applied to a PD10 column (LKB-Pharmacia) to remove lower molecular weight compounds. The column had been equilibrated with water before the 2.5 ml of the supernatant are applied and higher molecular weight compounds were then eluted with 3.5 ml of water. The elute was further purified by adding ion exchange beads (AG 501 X8, Biorad) and shaking for 30 minutes. After centrifugation at 4000 Rpm (Minifuge, Beckman) to remove the beads, the supernatant is applied to a Sepharose 4B column (diameter 16 cm, separating volume 24 ml) to remove the short sugar chains. The elute is vacuum dried in a vacuum centrifuge (univapo 150 H, Uniquip, Martinsried (FRG) and than analysed by 13C-NMR under the following conditions:

    ______________________________________                                         PULPROG zgdc30       F2-Processing                                                                  parameters                                                SOLVENT D20          SI         32768                                          AQ      1.3762726 sec                                                                               SF         100.5485322 MHz                                FIDRES  0.363305 Hz  WDW        EM                                             DW      21.0 usec    SSB        0                                              RG      32768        LB         0.50 Hz                                        NUCLEUS 13 C         GB         0                                              D11     0.0300000 sec                                                                               PC         1.40                                           P31     100.0 usec                                                             S2      20 dB        10 NMR plot                                                                    parameters                                                HL1     1 dB         CX         33.00 cm                                       D1      1.0000000 sec                                                                               F1P        123.000 ppm                                    P1      6.5 usec     F1         12367.47 Hz                                    DE      26.3 usec    F2P        -6.000 ppm                                     SF01    100.5597430 MHz                                                                             F2         -603.29 Hz                                     SWH     23809.58 Hz  PPMCM      3.90909 ppm/cm                                 TD      65536        HZCM       393.05334 Hz/cm                                NS      8000                                                                   DS      2                                                                      ______________________________________                                    

The result of the analysis is shown in FIG. 5. The pattern of NMR peaks obtained is the same as it is obtained for levan as published by Gross et al., 1992, Physiol Mol Plant Pathol 40: 371.

This proves that the transformed plants synthesise levan after transformation by one of the constructs described in examples 1 to 3.

    __________________________________________________________________________     SEQUENCE LISTING                                                               (1) GENERAL INFORMATION:                                                       (iii) NUMBER OF SEQUENCES: 2                                                   (2) INFORMATION FOR SEQ ID NO:1:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 1438 base pairs                                                    (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: DNA (genomic)                                              (iii) HYPOTHETICAL: NO                                                         (iv) ANTI-SENSE: NO                                                            (vi) ORIGINAL SOURCE:                                                          (A) ORGANISM: Erwinia amylovora                                                (C) INDIVIDUAL ISOLATE: Strain Ea/74m                                          (G) CELL TYPE: bacterium                                                       (vii) IMMEDIATE SOURCE:                                                        (A) LIBRARY: genomic                                                           (B) CLONE: DH5alpha pEA-LS5                                                    (ix) FEATURE:                                                                  (A) NAME/KEY: CDS                                                              (B) LOCATION: 155..1399                                                        (D) OTHER INFORMATION: /note= "Levansucrase"                                   (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:                                        GGATCCCCCGGGCTGCAGCGATCATGGTTATTTATAAGGGATTGTTATGTCCTGAAAACC60                 ACACAACAGAACCAGAGTGATTTCAAAAAATAAAAAGCTATTAATATACAGACCTTCAGC120                AAGAAGGTATTCGAAATAACCTGTGAGGATATTTATGTCAGATTATAATTAT172                        MetSerAspTyrAsnTyr                                                             15                                                                             AAACCAACGCTGTGGACTCGTGCCGATGCATTGAAAGTTCATGAGGAT220                            LysProThrLeuTrpThrArgAlaAspAlaLeuLysValHisGluAsp                               101520                                                                         GACCCAACCACAACTCAACCGGTTATTGACATTGCATTCCCGGTAATG268                            AspProThrThrThrGlnProValIleAspIleAlaPheProValMet                               253035                                                                         AGTGAAGAAGTCTTTATTTGGGATACCATGCCATTGCGAGACTTCGAC316                            SerGluGluValPheIleTrpAspThrMetProLeuArgAspPheAsp                               404550                                                                         GGAGAGATTATCTCTGTAAATGGTTGGTGTATTATTTTTACGCTAACA364                            GlyGluIleIleSerValAsnGlyTrpCysIleIlePheThrLeuThr                               55606570                                                                       GCAGATCGCAACACTGATAATCCGCAATTCCAGGATGAAAATGGCAAT412                            AlaAspArgAsnThrAspAsnProGlnPheGlnAspGluAsnGlyAsn                               758085                                                                         TATGATATTACTCGTGACTGGGAAGACAGACATGGTCGTGCGCGTATT460                            TyrAspIleThrArgAspTrpGluAspArgHisGlyArgAlaArgIle                               9095100                                                                        TGTTATTGGTACTCACGCACCGGTAAAGACTGGATTTTTGGCGGTCGG508                            CysTyrTrpTyrSerArgThrGlyLysAspTrpIlePheGlyGlyArg                               105110115                                                                      GTAATGGCCGAAGGTGTCGCACCGACGACGCGTGAGTGGGCCGGAACC556                            ValMetAlaGluGlyValAlaProThrThrArgGluTrpAlaGlyThr                               120125130                                                                      CCGATCCTTTTAAACGATCGGGGCGATATTGACCTGTATTATACCTGT604                            ProIleLeuLeuAsnAspArgGlyAspIleAspLeuTyrTyrThrCys                               135140145150                                                                   GTCACTCCGGGTGCAACCATTGCCAAAGTGCGCGGTAAAATCGTCACT652                            ValThrProGlyAlaThrIleAlaLysValArgGlyLysIleValThr                               155160165                                                                      TCCGATCAAAGTGTAAGCCTGGAAGGTTTTCAGCAGGTTACATCACTT700                            SerAspGlnSerValSerLeuGluGlyPheGlnGlnValThrSerLeu                               170175180                                                                      TTCTCTGCTGACGGGACTATTTACCAGACGGAAGAGCAGAACGCTTTC748                            PheSerAlaAspGlyThrIleTyrGlnThrGluGluGlnAsnAlaPhe                               185190195                                                                      TGGAACTTCCGTGACCCAAGCCCATTCATTGACAGGAATGATGGCAAA796                            TrpAsnPheArgAspProSerProPheIleAspArgAsnAspGlyLys                               200205210                                                                      TTATATATGCTGTTTGAAGGAAACGTGGCGGGGCCGCGCGGTTCGCAC844                            LeuTyrMetLeuPheGluGlyAsnValAlaGlyProArgGlySerHis                               215220225230                                                                   GAAATTACCCAGGCTGAGATGGGTAATGTGCCGCCGGGTTATGAAGAT892                            GluIleThrGlnAlaGluMetGlyAsnValProProGlyTyrGluAsp                               235240245                                                                      GTGGGTGGCGCAAAATATCAGGCAGGCTGTGTTGGTCTGGCTGTGGCC940                            ValGlyGlyAlaLysTyrGlnAlaGlyCysValGlyLeuAlaValAla                               250255260                                                                      AAAGACCTGTCAGGCAGTGAGTGGCAAATCCTGCCTCCGCTGATCACC988                            LysAspLeuSerGlySerGluTrpGlnIleLeuProProLeuIleThr                               265270275                                                                      GCTGTTGGCGTAAACGATCAGACTGAACGCCCTCATTTTGTCTTCCAG1036                           AlaValGlyValAsnAspGlnThrGluArgProHisPheValPheGln                               280285290                                                                      GATGGTAAATACTATCTGTTCACCATTAGCCATAAGTACACTTTTGCC1084                           AspGlyLysTyrTyrLeuPheThrIleSerHisLysTyrThrPheAla                               295300305310                                                                   GATAACCTGACCGGCCCTGATGGAGTGTATGGCTTTGTAAGCGATAAA1132                           AspAsnLeuThrGlyProAspGlyValTyrGlyPheValSerAspLys                               315320325                                                                      CTTACCGGCCCTTACACGCCGATGAATAGCTCCGGGCTGGTGCTGGGC1180                           LeuThrGlyProTyrThrProMetAsnSerSerGlyLeuValLeuGly                               330335340                                                                      AACCCGTCTTCACAACCTTTCCAGACATATTCACACTATGTTATGCCT1228                           AsnProSerSerGlnProPheGlnThrTyrSerHisTyrValMetPro                               345350355                                                                      AATGGGCTGGTCACTTCCTTTATTGACAGTGTTCCGTGGAAAGGTAAG1276                           AsnGlyLeuValThrSerPheIleAspSerValProTrpLysGlyLys                               360365370                                                                      GACTATCGCATTGGCGGTACTGAAGCTCCGACCGTAAAAATTCTGTTG1324                           AspTyrArgIleGlyGlyThrGluAlaProThrValLysIleLeuLeu                               375380385390                                                                   AAAGGCGATCGCTCATTTATTGTTGATAGCTTCGATTATGGATATATT1372                           LysGlyAspArgSerPheIleValAspSerPheAspTyrGlyTyrIle                               395400405                                                                      CCGGCAATGAAAGACATTACTTTAAAATAAGTCTGTTGTCGATATCA1419                            ProAlaMetLysAspIleThrLeuLys                                                    410415                                                                         AGCTTATCGATACCGTCGA1438                                                        (2) INFORMATION FOR SEQ ID NO:2:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 415 amino acids                                                    (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: protein                                                    (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:                                        MetSerAspTyrAsnTyrLysProThrLeuTrpThrArgAlaAspAla                               151015                                                                         LeuLysValHisGluAspAspProThrThrThrGlnProValIleAsp                               202530                                                                         IleAlaPheProValMetSerGluGluValPheIleTrpAspThrMet                               354045                                                                         ProLeuArgAspPheAspGlyGluIleIleSerValAsnGlyTrpCys                               505560                                                                         IleIlePheThrLeuThrAlaAspArgAsnThrAspAsnProGlnPhe                               65707580                                                                       GlnAspGluAsnGlyAsnTyrAspIleThrArgAspTrpGluAspArg                               859095                                                                         HisGlyArgAlaArgIleCysTyrTrpTyrSerArgThrGlyLysAsp                               100105110                                                                      TrpIlePheGlyGlyArgValMetAlaGluGlyValAlaProThrThr                               115120125                                                                      ArgGluTrpAlaGlyThrProIleLeuLeuAsnAspArgGlyAspIle                               130135140                                                                      AspLeuTyrTyrThrCysValThrProGlyAlaThrIleAlaLysVal                               145150155160                                                                   ArgGlyLysIleValThrSerAspGlnSerValSerLeuGluGlyPhe                               165170175                                                                      GlnGlnValThrSerLeuPheSerAlaAspGlyThrIleTyrGlnThr                               180185190                                                                      GluGluGlnAsnAlaPheTrpAsnPheArgAspProSerProPheIle                               195200205                                                                      AspArgAsnAspGlyLysLeuTyrMetLeuPheGluGlyAsnValAla                               210215220                                                                      GlyProArgGlySerHisGluIleThrGlnAlaGluMetGlyAsnVal                               225230235240                                                                   ProProGlyTyrGluAspValGlyGlyAlaLysTyrGlnAlaGlyCys                               245250255                                                                      ValGlyLeuAlaValAlaLysAspLeuSerGlySerGluTrpGlnIle                               260265270                                                                      LeuProProLeuIleThrAlaValGlyValAsnAspGlnThrGluArg                               275280285                                                                      ProHisPheValPheGlnAspGlyLysTyrTyrLeuPheThrIleSer                               290295300                                                                      HisLysTyrThrPheAlaAspAsnLeuThrGlyProAspGlyValTyr                               305310315320                                                                   GlyPheValSerAspLysLeuThrGlyProTyrThrProMetAsnSer                               325330335                                                                      SerGlyLeuValLeuGlyAsnProSerSerGlnProPheGlnThrTyr                               340345350                                                                      SerHisTyrValMetProAsnGlyLeuValThrSerPheIleAspSer                               355360365                                                                      ValProTrpLysGlyLysAspTyrArgIleGlyGlyThrGluAlaPro                               370375380                                                                      ThrValLysIleLeuLeuLysGlyAspArgSerPheIleValAspSer                               385390395400                                                                   PheAspTyrGlyTyrIleProAlaMetLysAspIleThrLeuLys                                  405410415                                                                      __________________________________________________________________________ 

We claim:
 1. A method of producing a transgenic plant with modified polyfructan formation comprising the following steps:(a) preparing a DNA molecule which comprises the following sequences:i) a promoter which is active in plants and ensures formation of RNA in a predetermined target tissue or target cell, ii) a DNA sequence encoding a polyfructan sucrase, wherein said DNA sequence is derived from Erwinia amylovora, and iii) a 3'-non-translated sequence, which in a plant cell leads to the termination of transcription as well as the addition of a poly-A-tail to the 3'-end of the RNA, (b) transferring said DNA molecule into a plant cell thereby producing a transformed plant cell, and (c) regenerating an intact, whole plant from the transformed plant cell which expresses the DNA sequence.
 2. A method for the production of a transgenic plant with modified polyfructan formation comprising the following steps:(a) preparing a DNA molecule which comprises the following sequences:(i) a promoter which is active in plants and ensures formation of RNA in mined target tissue or cell: (ii) a DNA sequence encoding a polyfructan sucrase which comprises: ##STR2## and (iii) a 3'-non-translated sequence. which in a plant cell leads to the termination of transcription as well as to the addition of a poly-A-tail to the 3'-end of the RNA; (b) transferring said DNA molecule into a plant cell thereby producing a transformed plant cell: and (c) regenerating an intact, whole plant from the transformed plant cell which expresses the DNA sequence.
 3. A process according to claim 2, wherein the polyfructan sucrase expression leads to polyfructan sucrase activity in a predetermined area of a plant selected from the group consisting of chloroplasts, amyloplasts, mitochondria, cytosol, intercellular space and vacuoles.
 4. A plant obtainable by the process according to claim
 1. 5. A plant according to claim 4, wherein said plant is a crop plant.
 6. A plant according to claim 5, wherein said plant is selected from the group consisting of maize, rice, wheat, barley, sugar cane, tobacco and potato.
 7. A method of producing a plant with modified polyfructan formation, comprising the step of utilizing a DNA sequence coding for a polyfructan sucrase from Erwinia amylovora to transform a plant.
 8. A method of producing a plant with modified polyfructan formation, comprising the step of utilizing a plasmid selected from the group consisting of p35s-Cw-LEV (DSM 7186), plasmid p35s-Cy-LEV (DSM 7187) and plasmid p33-Cw-LEV (DSM 7188) to transform a plant.
 9. A plant obtainable by the process according to claim
 3. 10. A process, according to claim 1, wherein the polyfructan sucrase expression leads to polyfructan sucrase activity in a predetermined area of a plant selected from the group consisting of chloroplasts, amyloplasts, mitochondria, cytosol, intercellular space and vacuoles.
 11. A plant obtainable by the process according to claim
 2. 12. A plant obtainable by the process according to claim
 7. 13. A plant obtainable by the process according to claim
 8. 14. A method of producing a plant with modified polyfructan formation, comprising the step of utilizing a DNA sequence comprising the coding region of SEQ ID No. 1 to transform the plant so that the iplant contains and expresses the DNA sequence.
 15. A plant obtainable by the process according to claim
 14. 16. A plant or plant cell each transformed with a DNA sequence coding for a polyfructan sucrase from Erwinia amylovora, wherein said plant or plant cell is capable of expressing an altered amount of polyfructan sucrase activity relative to a non-transformed plant.
 17. A plant or plant cell each transformed with a DNA sequence which comprises SEQ ID No. 1, wherein said plant or plant cell is capable of expressing an altered amount of polyfructan sucrase activity relative to a non-transformed plant.
 18. A method for producing a transgenic plant with modified polyfructan formation comprising:transforming a plant cell so as to contain and express an isolated DNA molecule encoding a polyfructan sucrase in a predetermined target tissue wherein the isolated DNA molecule is derived from Ezwinia amylovora; and regenerating an intact whole plant from the cell which contains and expresses the isolated DNA molecule.
 19. The method of any one of claims 1, 2, or 18, wherein the polyfructan sucrase expression leads to polyfructan sucrase activity in chloroplasts of the plant.
 20. The method of any one of claims 1, 2, or 18, wherein the polyfructan sucrase expression leads to polyfructan sucrase activity in amyloplasts of the plant.
 21. The method of any one of claims 1, 2, or 18, wherein the polyfructan sucrase expression leads to polyfructan sucrase activity in vacuoles of the plant.
 22. The method of any one of claims 1, 2, or 18, wherein the polyfructan sucrase expression leads to polyfructan sucrase activity in mitochondria of the plant.
 23. A plant obtainable from the process of claim
 18. 24. A plant obtainable from the process of claim
 19. 25. A plant obtainable from the process of claim
 20. 26. A plant obtainable from the process of claim
 21. 27. A plant obtainable from the process of claim
 22. 28. The plant of claim 23 which is a crop plant.
 29. The plant of claim 24 which is a crop plant.
 30. The plant of claim 25 which is a crop plant.
 31. The plant of claim 26 which is a crop plant.
 32. The plant of claim 27 which is a crop plant. 